Phoenix on the Rocks

As seen in the top center of this image from Phoenix, the exhaust from the descent engine has blown soil off to reveal either rock or ice, which has not yet been determined.Credit:NASA/JPL-Caltech/University of Arizona.

Scientists have discovered what may be ice that was exposed when soil was blown away as NASA’s Phoenix spacecraft landed on Mars last Sunday, May 25. The possible ice appears in an image the robotic arm camera took underneath the lander, near a footpad.

"We could very well be seeing rock, or we could be seeing exposed ice in the retrorocket blast zone," said Ray Arvidson of Washington University, St. Louis, Mo., co-investigator for the robotic arm. "We’ll test the two ideas by getting more data, including color data, from the robotic arm camera. We think that if the hard features are ice, they will become brighter because atmospheric water vapor will collect as new frost on the ice."

"Full confirmation of what we’re seeing will come when we excavate and analyze layers in the nearby workspace," Arvidson said. Testing of a Phoenix instrument that bakes and sniffs samples to identify ingredients identified a possible short circuit. This prompted commands for diagnostic steps to be developed and sent to the lander in the next few days. The instrument is the Thermal and Evolved Gas Analyzer. It includes a calorimeter that tracks how much heat is needed to melt or vaporize substances in a sample, plus a mass spectrometer to examine vapors driven off by the heat. The Thursday, May 29, tests recorded electrical behavior consistent with an intermittent short circuit in the spectrometer portion.

This approximate color (red, green, and blue filters: 600, 530, and 480 nanometers) view was obtained on sol 2 by the Surface Stereo Imager on board the Phoenix lander. The view is toward the northwest, showing polygonal terrain near the lander and out to the horizon. Credit:NASA/JPL-Caltech/University of Arizona.

"We have developed a strategy to gain a better understanding of this behavior, and we have identified workarounds for some of the possibilities," said William Boynton of the University of Arizona, Tucson, lead scientist for the instrument.

The latest data from the Canadian Space Agency’s weather station shows another sunny day at the Phoenix landing site with temperatures holding at minus 30 degrees Celsius (minus 22 degrees Fahrenheit) as the sol’s high, and a low of minus 80 degrees Celsius (minus 112 degrees Fahrenheit). The lidar instrument was activated for a 15-minute period just before noon local Mars time, and showed increasing dust in the atmosphere.

"This is the first time lidar technology has been used on the surface of another planet," said the meteorological station’s chief engineer, Mike Daly, from MDA in Brampton, Canada. "The team is elated that we are getting such interesting data about the dust dynamics in the atmosphere."

The mission passed a "safe to proceed" review on Thursday evening, meeting criteria to proceed with evaluating and using the science instruments.

"We have evaluated the performance of the spacecraft on the surface and found we’re ready to move forward. While we are still investigating instrument performance such as the anomaly on TEGA [Thermal and Evolved Gas Analyzer], the spacecraft’s infrastructure has passed its tests and gets a clean bill of health," said David Spencer of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., deputy project manager for Phoenix.

"We’re still in the process of checking out our instruments," Phoenix project scientist Leslie Tamppari of JPL said. "The process is designed to be very flexible, to respond to discoveries and issues that come up every day. We’re in the process of taking images and getting color information that will help us understand soil properties. This will help us understand where best to first touch the soil and then where and how best to dig."

May 31 Update:

The Robotic Arm Camera captured this image underneath the Phoenix lander on the fifth Martian day, or sol, of the mission. Descent thrusters on the bottom of the lander are visible at the top of the image. The abundance of excavated smooth and level surfaces adds evidence to a hypothesis that the underlying material is an ice table covered by a thin blanket of soil. Click image for larger view.Credit:NASA/JPL-Caltech/University of Arizona.

A view of the ground underneath NASA’s Phoenix Mars Lander adds to evidence that descent thrusters dispersed overlying soil and exposed a harder substrate that may be ice. The image received Friday night from the spacecraft’s Robotic Arm Camera shows patches of smooth and level surfaces beneath the thrusters.

"This suggests we have an ice table under a thin layer of loose soil," said the lead scientist for the Robotic Arm Camera, Horst Uwe Keller of Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

"We were expecting to find ice within two to six inches of the surface," said Peter Smith of the University of Arizona, Tucson, principal investigator for Phoenix. "The thrusters have excavated two to six inches and, sure enough, we see something that looks like ice. It’s not impossible that it’s something else, but our leading interpretation is ice."